Within the past decade the price of crude oil, the basis for most petroleum products, has increased significantly; in addition its availability in needed quantities has at times been severely curtailed. This has created many problems to the manufacturers and consumers leading to attempts to reduce reliance on crude oil as the basic starting material. A major product dependent on adequate supplies of crude oil is ethanol, which has been manufactured in significant quantities by the hydration of ethylene derived from petroleum or crude oil. The increased costs of crude oil are, however, making this process less economical at a time when the demand for ethanol for use in fuels, such as gasohol, or as an intermediate for producing other organic compounds, such as ethylene (from dehydration), is increasing at an unpredictable rate. Thus, much effort is being expended to the development of alternate processes for the production of ethanol at economically acceptable costs from other sources.
While the production of ethanol by the well known fermentation process is well established, this process competes with the use of the starting materials generally used, grains and sugars, as foodstuffs. Further, in many instances the feedstocks are not readily available at the plant site and the processes are multi-step procedures requiring provisions for fermentation, distillation and disposal of residual solid wastes. To attempt to supply the anticipated demand for ethanol solely by additional fermentation plants could result in a significant disruption in the amount of feed grain available for human needs. As a result methods which do not severely disrupt these needs are preferred.
Such procedures involve the use of synthesis gas, a mixture of carbon monoxide and hydrogen. This is an alternate feedstock which is inexpensive and increasingly desirable because it can be derived from non-petroleum sources such as coal.
Among the references relating to the production of organic compounds, including ethanol, of particular interest are those using complexes containing cobalt or osmium or ruthenium compounds as a component of the catalyst complex in the reaction of synthesis gas. Basically the known processes involve the catalytic homologation of methanol with synthesis gas at elevated temperatures and pressures, with most processes yielding a mixture of products that are subsequently separated. To our present knowledge there is no single reference that can be said to individually teach how to selectively produce ethanol at commercially significant efficiencies directly from synthesis gas.
The direct, homogeneous conversion of synthesis gas to produce some ethanol is discussed in U.S. Pat. No. 2,534,018 issued to W. F. Gresham on Dec. 12, 1950. In this disclosure a cobalt-based catalyst and high pressures are used.
In U.S. Pat. No. 2,535,060 issued to W. F. Gresham on Dec. 26, 1950, there is described a process for preparing mixtures of monohydric alcohols by the reaction of a mixture of carbon monoxide, hydrogen and a hydroxylated solvent at a temperature of from 150.degree. C. to 300.degree. C. and a pressure of from 200 to 1,000 atmospheres using a ruthenium-containing catalyst and an alkaline reagent to control pH within the range of 7 to 11.5. The reference clearly states that it is essential that the reaction take place in the liquid phase and that water and any alcohol can be used as the liquid reaction medium; it also mentions that experimental evidence indicates that the liquid reaction medium may participate in the reaction. The chief products obtained are hydroxyalkanes having from 2 to 10 carbon atoms but there does not seem to be any indication of selectivity to any one specific alkanol.
A closely related reference is U.S. Pat. No. 2,549,470 issued to B. W. Howk et al on Apr. 17, 1951, which claims a process for selectively producing straight chain alkanols having from 3 to 50 carbon atoms by the liquid phase reaction of a mixture of carbon monoxide, hydrogen and a hydroxylated solvent at a temperature of from 100.degree. C. to 250.degree. C. and a pressure of from 200 to 1,000 atmospheres using a ruthenium-containing catalyst. These examples do show the production of small amounts of methanol and ethanol but the process essentially selectively produces the higher alkanols.
In U.S. Pat. No. 2,636,046 issued to W. F. Gresham on Apr. 21, 1953 there is discussed a direct, homogeneous process for producing ethanol from synthesis gas at low selectivities using cobalt-based catalysts and high pressures.
A cobalt-based catalyst is used in U.S. Pat. No. 3,248,432 issued to A. D. Riley et al on Apr. 26, 1966, to produce ethanol. In this reference methanol is reacted with carbon monoxide and hydrogen at a pressure in excess of 3,000 to 4,000 psi and a temperature of from about 150.degree. C. to 250.degree. C. in the presence of a modified catalyst complex containing cobalt, an iodine promoter and a phosphorus compound as defined. In essence this is an homologation process using a cobalt-based catalyst.
Another homologation process is disclosed in U.S. Pat. No. 3,285,948 issued to C. N. Butter et al on Nov. 15, 1966. This patent discloses the use of halides of ruthenium and osmium as second promoters in conjunction with cobalt and iodine for the production of ethanol by the homologation reaction of methanol with carbon monoxide and hydrogen.
The invention claimed in U.S. Pat. No. 3,387,043 issued to M. Kuraishi et al on June 4, 1968 is the improvement of adding water to the homologation reaction of ethanol, n-propanol or n-butanol with carbon monoxide and hydrogen using a catalyst containing cobalt and iodine.
The heterogeneous reaction of synthesis gas to produce ethanol at selectivities of less than 40 mole percent is discussed in U.S. Pat. No. 2,490,488 issued to S. G. Stewart on Dec. 6, 1949. In this patent the catalyst was molybdenum disulfide and an alkaline compound of an alkali metal.
A solid, heterogeneous catalyst is used in the homologation reaction disclosed in U.S. Pat. No. 3,972,952 issued to R. T. Clark on Aug. 3, 1976. The catalytic agent is a base promoter such as an oxide, hydroxide or salt of the alkali and alkaline earth metals and a metal of the group ruthenium, rhodium, palladium, osmium, iridium and platinum on an inert solid support material comprising alumina. In this process an alkanol is converted to a higher alkanol.
In U.S. Pat. No. 4,111,837 issued to P. D. Taylor on Sept. 5, 1978, methanol is reacted in liquid phase with carbon monoxide and hydrogen at a temperature of from 100.degree. C. to 350.degree. C. and a pressure of from 1,000 to 15,000 psi in the presence of a heterogeneous catalyst containing a cobalt derivative and a methanol-insoluble rhenium derivative.
Another heterogeneous reaction using a mixture of four essential elements (1) copper, (2) cobalt, (3) chromium, iron, vanadium or maganese, and (4) an alkali metal in the catalyst to convert synthesis gas to ethanol is described in U.S. Pat. No. 4,122,110 issued to A. Sugier et al on Oct. 24, 1978. In this process the selectivity is below 40 weight percent.
The homologation of methanol with carbon monoxide and hydrogen to produce ethanol is described in U.S. Pat. No. 4,133,966 issued to W. R. Pretzer et al on Jan. 9, 1979. In the process disclosed the catalyst system is cobalt acetylacetonate a tertiary organo Group VA--compound, an iodine compound as a first promoter and ruthenium compound as a second promoter. While the reaction is said to be selective to the production of ethanol, the experimental data fails to show any selectivity values greater than 60 mole percent.
The use of rhodium in combination with thorium and/or uranium to produce two-carbon atom oxygenated products from synthesis gas using a heterogeneous catalyst is disclosed in U.S. Pat. No. 4,162,262 issued to P. C. Ellgen et al on July 24, 1979. This patent stresses the minimization of methanol coproduction.
The homologation of methanol with synthesis gas in the liquid phase using a cobalt carbonyl catalyst is disclosed in U.S. Pat. No. 4,168,391 issued to W. E. Slinkard et al on Sept. 18, 1979. The improvement claimed in this patent is the use of a non-polar, substantially inert, oxygenated hydrocarbon solven that does not coordinate strongly with cobalt carbonyl as the solvent during the reaction.
A ruthenium based catalyst is disclosed in U.S. Pat. No. 4,170,605 issued to R. C. Williamson et al on Oct. 9, 1979; however, the process is one which selectively produces ethylene glycol, not alkanols.
Homologation is also disclosed in U.S. Pat. No. 4,190,729 issued to D. Foster on Feb. 26, 1980, in which a tertiary phosphine oxide is used as a stabilizer during the homologation reaction of methanol to ethanol, acetaldehyde and methyl acetate employing a cobalt-based catalyst.
The selective production of ethanol by the homologation of methanol with carbon monoxide and hydrogen under selected ratios and reaction conditions catalyzed by cobalt, ruthenium, an iodine promoter, and a phosphine ligand is shown in commonly assigned patent application Ser. No. 91,241, filed on Nov. 15, 1979 by R. A. Fiato.
In another commonly assigned patent application, Ser. No. 91,242, filed on Nov. 15, 1979 by B. D. Dombek, there is disclosed a process for selectively converting synthesis gas to ethylene glycol, ethanol and methanol using a homogeneous ruthenium carbonyl complex as the catalyst and a solvent which has a dielectric constant of at least 2 determined at 25.degree. C. or at its melting point, whichever is higher; the process also contemplates the use of a Lewis base promoter.
As is evident from the above, there is little existing prior art concerned with the direct selective production of ethanol from synthesis gas. In most instances ethanol is produced by homologation reactions, not directly, and in those instances in which a direct process is disclosed the process was not a homogeneous process or the ethanol selectivities and efficiencies achieved are not commercially acceptable.